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Showing content from https://www.geeksforgeeks.org/java/copyonwritearrayset-add-method-in-java/ below:

CopyOnWriteArraySet add() method in Java

Last Updated : 11 Jul, 2025

The

add(E e)

method of

CopyOnWriteArraySet

inserts the element passed in the parameter to the end of the Set or at a specified index in the Set. The function returns true on addition of new element to the Set.

Syntax:

public boolean add(E e)

Parameters:

The function accepts a single mandatory parameter

element

which specifies the element to be added in the Set.

Return Value:

The function returns

true

on addition in the Set. Below programs illustrate the above function:

Program 1: Java


 // Java Program to illustrate the CopyOnWriteArraySet
// add(element) method in Java

import java.util.concurrent.CopyOnWriteArraySet;
import java.util.*;

public class GFG {
    public static void main(String[] args)
    {

        // create object of CopyOnWriteArraySet
        CopyOnWriteArraySet<Integer> ArrSet
            = new CopyOnWriteArraySet<Integer>();

        // Add elements
        ArrSet.add(2);
        ArrSet.add(3);
        ArrSet.add(4);
        ArrSet.add(7);

        // print CopyOnWriteArraySet
        System.out.println("CopyOnWriteArraySet: "
                           + ArrSet);

        // 4 is already present hence cannot add
        System.out.println("On adding 4 it returns "
                           + ArrSet.add(4));

        // print CopyOnWriteArraySet
        System.out.println("Updated CopyOnWriteArraySet: "
                           + ArrSet);
    }
}

Output:

CopyOnWriteArraySet: [2, 3, 4, 7]
On adding 4 it returns false
Updated CopyOnWriteArraySet: [2, 3, 4, 7]

Program 2: Java


 // Java Program to illustrate the CopyOnWriteArraySet
// add(element) method in Java

import java.util.concurrent.CopyOnWriteArraySet;
import java.util.*;

public class GFG {
    public static void main(String[] args)
    {

        // create object of CopyOnWriteArraySet
        CopyOnWriteArraySet<Integer> ArrSet
            = new CopyOnWriteArraySet<Integer>();

        // Add elements
        ArrSet.add(2);
        ArrSet.add(3);
        ArrSet.add(3);
        ArrSet.add(3);

        // print CopyOnWriteArraySet
        System.out.println("CopyOnWriteArraySet: "
                           + ArrSet);

        // 45 is not present hence add
        System.out.println("On adding 45 it returns "
                           + ArrSet.add(45));

        // print CopyOnWriteArraySet
        System.out.println("Updated CopyOnWriteArraySet: "
                           + ArrSet);
    }
}

Output:

CopyOnWriteArraySet: [2, 3]
On adding 45 it returns true
Updated CopyOnWriteArraySet: [2, 3, 45]

Reference: https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/CopyOnWriteArraySet.html#add-E-

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